New publication First purely observation-based partitioning of urban CO₂ fluxes into fossil and non-fossil components in Paris, Munich and Zurich
Within the ICOS Cities project, and with the participation of researchers from Heidelberg University (IUP), urban CO₂ fluxes were experimentally partitioned into fossil and non-fossil components for the first time. For this purpose, radiocarbon (14C) measurements from the ICOS Central Radiocarbon Laboratory were combined with the relaxed eddy accumulation (REA) method. The results from 252 hour-long REA measurements showed that fossil sources dominated urban CO₂ fluxes, particularly in winter: In Munich, around 75 % of the CO₂ fluxes analysed in winter were of fossil origin, while in Zurich, the fossil contribution exceeded 90 %. In addition, the measurements revealed that current emission inventories do not fully capture all relevant source types. For example, contributions from non-fossil CO₂—such as emissions from breweries—were identified that are not or only insufficiently represented in existing inventories. The study highlights the importance of observation-based approaches for the independent quantification of urban emissions and provides valuable input for improving emission inventories and future monitoring strategies in the context of climate mitigation efforts.
Kunz, A.-K. and Hammer, S. and Aigner, P. and Bignotti, L. and Borchardt, L. and Chen, J. and Della Coletta, J. and Emmenegger, L. and Eritt, M. and Gutiérrez, X. and Hashemi, J. and Hilland, R. and Holst, C. and Jordan, A. and Kljun, N. and Kneißl, R. and Lan, C. and Legendre, V. and Levin, I. and Loubet, B. and Mauder, M. and Molinier, B. and Preunkert, S. and Ramonet, M. and Stagakis, S. and Christen, A. : 14C-based separation of fossil and non-fossil CO2 fluxes in cities using relaxed eddy accumulation: results from tall-tower measurements in Zurich, Paris, and Munich, Atmos. Chem. Phys., 26(7), 4967–5003, 2026.